On 11/06/2017 03:34 PM, Thadeu Lima de Souza Cascardo wrote:
> From: Mahesh Salgaonkar <mah...@linux.vnet.ibm.com>
>
> The kernel boot parameter 'nr_cpus=' allows one to specify number of
> possible cpus in the system. In the normal scenario the first cpu (cpu0)
> that shows up is the boot cpu and hence it gets covered under nr_cpus
> limit.
>
> But this assumption will be broken in kdump scenario where kdump kenrel
Minor nit: s/kenrel/kernel
> after a crash can boot up on an non-zero boot cpu. The paca structure
> allocation depends on value of nr_cpus and is indexed using logical cpu
> ids. This definetly will be an issue if boot cpu id > nr_cpus
Minor nit (2): s/definetly/definitely
>
> This patch modifies allocate_pacas() and smp_setup_cpu_maps() to
> accommodate boot cpu for the case where boot_cpuid > nr_cpu_ids.
>
> This change would help to reduce the memory reservation requirement for
> kdump on ppc64.
>
> Signed-off-by: Mahesh Salgaonkar <mah...@linux.vnet.ibm.com>
> Signed-off-by: Thadeu Lima de Souza Cascardo <casca...@canonical.com>
Tested-by: Guilherme G. Piccoli <gpicc...@linux.vnet.ibm.com>
Without this patch, got a crash deterministically when booting with
nr_cpus=1 in P8 bare-metal. The patch fixes the issue...
Thanks,
Guilherme
> ---
>
> v3: fixup signedness or nr_cpus to match nr_cpu_ids
> and fix conflict due to change from %d to %u
>
> Resending this as it was not applied, and I can reproduce the issue with
> v4.14-rc8 when booting a kdump kernel after a crash that has been given
> nr_cpus=1 as a parameter. With this patch, I can't reproduce it anymore.
>
> ---
> arch/powerpc/include/asm/paca.h | 3 +++
> arch/powerpc/include/asm/smp.h | 1 +
> arch/powerpc/kernel/paca.c | 23 +++++++++++++++++-----
> arch/powerpc/kernel/prom.c | 39
> +++++++++++++++++++++++++++++++++++++-
> arch/powerpc/kernel/setup-common.c | 25 ++++++++++++++++++++++++
> 5 files changed, 85 insertions(+), 6 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/paca.h b/arch/powerpc/include/asm/paca.h
> index 04b60af027ae..ea0dbf2bbeef 100644
> --- a/arch/powerpc/include/asm/paca.h
> +++ b/arch/powerpc/include/asm/paca.h
> @@ -49,6 +49,9 @@ extern unsigned int debug_smp_processor_id(void); /* from
> linux/smp.h */
> #define get_lppaca() (get_paca()->lppaca_ptr)
> #define get_slb_shadow() (get_paca()->slb_shadow_ptr)
>
> +/* Maximum number of threads per core. */
> +#define MAX_SMT 8
> +
> struct task_struct;
>
> /*
> diff --git a/arch/powerpc/include/asm/smp.h b/arch/powerpc/include/asm/smp.h
> index fac963e10d39..553cd22b2ccc 100644
> --- a/arch/powerpc/include/asm/smp.h
> +++ b/arch/powerpc/include/asm/smp.h
> @@ -30,6 +30,7 @@
> #include <asm/percpu.h>
>
> extern int boot_cpuid;
> +extern int boot_hw_cpuid;
> extern int spinning_secondaries;
>
> extern void cpu_die(void);
> diff --git a/arch/powerpc/kernel/paca.c b/arch/powerpc/kernel/paca.c
> index 2ff2b8a19f71..9c689ee4b6a3 100644
> --- a/arch/powerpc/kernel/paca.c
> +++ b/arch/powerpc/kernel/paca.c
> @@ -207,6 +207,7 @@ void __init allocate_pacas(void)
> {
> u64 limit;
> int cpu;
> + unsigned int nr_cpus;
>
> limit = ppc64_rma_size;
>
> @@ -219,20 +220,32 @@ void __init allocate_pacas(void)
> limit = min(0x10000000ULL, limit);
> #endif
>
> - paca_size = PAGE_ALIGN(sizeof(struct paca_struct) * nr_cpu_ids);
> + /*
> + * Always align up the nr_cpu_ids to SMT threads and allocate
> + * the paca. This will help us to prepare for a situation where
> + * boot cpu id > nr_cpus_id. We will use the last nthreads
> + * slots (nthreads == threads per core) to accommodate a core
> + * that contains boot cpu thread.
> + *
> + * Do not change nr_cpu_ids value here. Let us do that in
> + * early_init_dt_scan_cpus() where we know exact value
> + * of threads per core.
> + */
> + nr_cpus = _ALIGN_UP(nr_cpu_ids, MAX_SMT);
> + paca_size = PAGE_ALIGN(sizeof(struct paca_struct) * nr_cpus);
>
> paca = __va(memblock_alloc_base(paca_size, PAGE_SIZE, limit));
> memset(paca, 0, paca_size);
>
> printk(KERN_DEBUG "Allocated %u bytes for %u pacas at %p\n",
> - paca_size, nr_cpu_ids, paca);
> + paca_size, nr_cpus, paca);
>
> - allocate_lppacas(nr_cpu_ids, limit);
> + allocate_lppacas(nr_cpus, limit);
>
> - allocate_slb_shadows(nr_cpu_ids, limit);
> + allocate_slb_shadows(nr_cpus, limit);
>
> /* Can't use for_each_*_cpu, as they aren't functional yet */
> - for (cpu = 0; cpu < nr_cpu_ids; cpu++)
> + for (cpu = 0; cpu < nr_cpus; cpu++)
> initialise_paca(&paca[cpu], cpu);
> }
>
> diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
> index f83056297441..93837093c5cb 100644
> --- a/arch/powerpc/kernel/prom.c
> +++ b/arch/powerpc/kernel/prom.c
> @@ -302,6 +302,29 @@ static void __init check_cpu_feature_properties(unsigned
> long node)
> }
> }
>
> +/*
> + * Adjust the logical id of a boot cpu to fall under nr_cpu_ids. Map it to
> + * last core slot in the allocated paca array.
> + *
> + * e.g. on SMT=8 system, kernel booted with nr_cpus=1 and boot cpu = 33,
> + * align nr_cpu_ids to MAX_SMT value 8. Allocate paca array to hold up-to
> + * MAX_SMT=8 cpus. Since boot cpu 33 is greater than nr_cpus (8), adjust
> + * its logical id so that new id becomes less than nr_cpu_ids. Make sure
> + * that boot cpu's new logical id is aligned to its thread id and falls
> + * under last nthreads slots available in paca array. In this case the
> + * boot cpu 33 is adjusted to new boot cpu id 1.
> + *
> + */
> +static inline void adjust_boot_cpuid(int nthreads, int phys_id)
> +{
> + boot_hw_cpuid = phys_id;
> + if (boot_cpuid >= nr_cpu_ids) {
> + boot_cpuid = (boot_cpuid % nthreads) + (nr_cpu_ids - nthreads);
> + pr_info("Adjusted logical boot cpu id: logical %d physical
> %d\n",
> + boot_cpuid, phys_id);
> + }
> +}
> +
> static int __init early_init_dt_scan_cpus(unsigned long node,
> const char *uname, int depth,
> void *data)
> @@ -325,6 +348,18 @@ static int __init early_init_dt_scan_cpus(unsigned long
> node,
>
> nthreads = len / sizeof(int);
>
> +#ifdef CONFIG_SMP
> + /*
> + * Now that we know threads per core lets align nr_cpu_ids to
> + * correct SMT value.
> + */
> + if (nr_cpu_ids % nthreads) {
> + nr_cpu_ids = _ALIGN_UP(nr_cpu_ids, nthreads);
> + pr_info("Aligned nr_cpus to SMT=%d, nr_cpu_ids = %d\n",
> + nthreads, nr_cpu_ids);
> + }
> +#endif
> +
> /*
> * Now see if any of these threads match our boot cpu.
> * NOTE: This must match the parsing done in smp_setup_cpu_maps.
> @@ -363,7 +398,9 @@ static int __init early_init_dt_scan_cpus(unsigned long
> node,
> DBG("boot cpu: logical %d physical %d\n", found,
> be32_to_cpu(intserv[found_thread]));
> boot_cpuid = found;
> - set_hard_smp_processor_id(found, be32_to_cpu(intserv[found_thread]));
> + adjust_boot_cpuid(nthreads, be32_to_cpu(intserv[found_thread]));
> + set_hard_smp_processor_id(boot_cpuid,
> + be32_to_cpu(intserv[found_thread]));
>
> /*
> * PAPR defines "logical" PVR values for cpus that
> diff --git a/arch/powerpc/kernel/setup-common.c
> b/arch/powerpc/kernel/setup-common.c
> index 2e3bc16d02b2..46b1e0972a20 100644
> --- a/arch/powerpc/kernel/setup-common.c
> +++ b/arch/powerpc/kernel/setup-common.c
> @@ -85,6 +85,7 @@ struct machdep_calls *machine_id;
> EXPORT_SYMBOL(machine_id);
>
> int boot_cpuid = -1;
> +int boot_hw_cpuid = -1;
> EXPORT_SYMBOL_GPL(boot_cpuid);
>
> /*
> @@ -473,6 +474,7 @@ void __init smp_setup_cpu_maps(void)
> struct device_node *dn = NULL;
> int cpu = 0;
> int nthreads = 1;
> + bool boot_cpu_added = false;
>
> DBG("smp_setup_cpu_maps()\n");
>
> @@ -499,6 +501,24 @@ void __init smp_setup_cpu_maps(void)
> }
>
> nthreads = len / sizeof(int);
> + /*
> + * If boot cpu hasn't been added to paca and there are only
> + * last nthreads slots available in paca array then wait
> + * for boot cpu to show up.
> + */
> + if (!boot_cpu_added && (cpu + nthreads) >= nr_cpu_ids) {
> + int found = 0;
> +
> + DBG("Holding last nthreads paca slots for boot cpu\n");
> + for (j = 0; j < nthreads && cpu < nr_cpu_ids; j++) {
> + if (boot_hw_cpuid == be32_to_cpu(intserv[j])) {
> + found = 1;
> + break;
> + }
> + }
> + if (!found)
> + continue;
> + }
>
> for (j = 0; j < nthreads && cpu < nr_cpu_ids; j++) {
> bool avail;
> @@ -514,6 +534,11 @@ void __init smp_setup_cpu_maps(void)
> set_cpu_present(cpu, avail);
> set_hard_smp_processor_id(cpu, be32_to_cpu(intserv[j]));
> set_cpu_possible(cpu, true);
> + if (boot_hw_cpuid == be32_to_cpu(intserv[j])) {
> + DBG("Boot cpu %d (hard id %d) added to paca\n",
> + cpu, be32_to_cpu(intserv[j]));
> + boot_cpu_added = true;
> + }
> cpu++;
> }
> }
>
